Because of your recklessness and simplicity in dealing with things, the present situation has been caused. Obviously, your method is wrong.
The question of whether to sell pyramid schemes is not something you can solve with a simple sentence. You have to sort out the ins and outs of the matter before you can come to this conclusion.
1. What's it like for his brother to open a shop in partnership with others? You know nothing about the name of the store, the contents of the products you handle, the sales channels, etc. The next conclusion is too simple.
Second, she said she could earn100000 in three years. Maybe this sentence is watery or exaggerated, or she doesn't know the specific profit target. Being with you is just an expression. The store she runs may be a serious investment, and it is a bit arbitrary for you to draw the conclusion of "pyramid selling" with only one sentence.
Third, if you don't fall for your girlfriend, you can go there to have a look, find out the situation, take photos, and check whether industrial and commercial registration, the tax situation, the salesman, the manager and the boss are realistic. It's not too late to wait for you to make a statement.
Now you should go to her mother to explain the situation, ask her not to scold her girlfriend, admit that she doesn't know the situation yet, and ask her brother for advice and talk about his concerns, hoping that he can help her sister solve it.
If you know that it is really a legitimate job, you should support your girlfriend to broaden her horizons and get exercise, and even you can go with her.
In a word, don't be subjective and arbitrary. All conclusions are based on careful investigation. No investigation, no right to speak, and talking nonsense will make things worse.